水素雰囲気による鋼の脱窒に関する研究

Abstract

A study of the removal of nitrogen from rimmed sheet steel and high carbon piano wire has been performed. The denitrogenizing annealing was carried out at temperatures from 500 to 1000°C in dry or wet hydrogen atmosphere and also in alternating atomspheres of dry hydrogen and vacuum. The following results were obtained.The rate of nitrogen removal from rimmed sheet steel containing 004 to 005% C is increased appreciably with increase in temperature up to about 700 to 720°C, where the gamma phase appears, while it is decreased with further increase in temperature. The rate of nitrogen removal is also increased with an increase in flow rate of hydrogen up to 350cc/min under the present experimental condition, but any more increase in the rate is hardly observed with further increase in the flow rate of hydrogen.When the flow rate of hydrogen is higher than 350cc/min under the present experimental condition, the rate of nitrogen removal is controlled by the diffusion of nitrogen in steel, and when the flow rate of hydrogen is lower than 100cc/min the rate of nitrogen removal follows the first order rate law, i.e., the logarithm of the ratio of nitrogen content to that of initial nitrogen is proportional to the time of treatment.The water vapor up to about 20 vol% in hydrogen of 350ccimin has no effect on the rate of nitrogen removal from sheet steel, and the water vapor up to about 2 to 5 vol% in hydrogen of 100cc/min has a slight effect to increase the rate of nitrogen removal while the rate is decreased with further increase in water vapor.Decarburization is not observed by dry hydrogen atmosphere while by the small addition of water vapor to hydrogen the rate and extent of decarburization are increased appreciably.Judging from the present experimental results and the previous investigations, it is concluded that 1) if the process of nitrogen removal is performed in hydrogen of high flow rate, the rate of nitrogen removal is controlled by the diffusion of nitrogen in steel while 2) if it is performed in hydrogen of low flow rate the rate of nitrogen removal is controlled by the rate of outgoing transfer of the gases produced by denitrogenizing reaction from the reaction chamber.It is suggested that the annealing by alternating treatment by hydrogen and vacuum can save the hydrogen consumption and the rapid and homogeneous nitrogen removal throughout the coil may be possible with a relatively small consumption of hydrogen when this technique is applied to the open coil annealing.